1. Field of the Invention
This invention relates to sewing machines and refers particularly, through not exclusively, to long-arm sewing machines created by extending the arm of standard sewing machines.
2. Description of the Related Art
When sewing fabrics of more than standard width a sewing machine having a longer arm is required. The arm of a sewing machine is that part which extends from the main body to the sewing head. Normally, the arm is extended by cutting the arm and inserting all necessary mechanisms and spacers to make the arm the necessary length. This has created several problems.
The principal problem is caused when the extended arm and/or the bed of the sewing machine flex so that the gap between the sewing head at the outermost end of the extended arm and the bed, varies. The flexing is due to the instability of the machine itself.
A second problem of an extended arm is the increased tendency to vibrate at the sewing head. If the variation in sewing height varies due to vibration, the machine can jam. With the vibrations induced in the operation of a sewing machine, it has been found that such arms have tended to allow for flexibility to the stage that the sewing head does move sufficiently to cause jamming of the sewing machine.
With the precision nature of high-speed sewing machines, particularly industrial sewing machines, a variation in the height of the sewing needle above the counter mechanism in the bed of the machine can cause misalignment of the sewing mechanisms or secure of the machine. The variation need only be as little as half a millimeter for this to occur.
Furthermore, with the distance of the sewing head from the body and the weight of the sewing head, the increased bending movement may cause the arm to bend slightly and thus displace the sewing head.
Also, most bodies of sewing machines are made as castings. With the vibration and the extra weight being placed upon the main body a cracking of the body may occur to the stage that a new body is required. This causes the machine to be removed from use and dismantled, with a significant loss of productivity.
In the past these problems have attempted to be overcome by installing bracing along the top of the arm to allow for greater rigidity. Such bracing is normally bolted to the top of the body. It has slightly reduced the vibration or movement of the head, but has increased significantly the cracking problem. However, vibration and movement still occurs.